Transformer bypass circuit



Feb. 16, 1960 E. J. Dl EBOLD 2,925, 7

TRANSFORMER BYPASS CIRCUIT Filed Sept. 17, 1956 5 Sheets-Sheet 1 ax/WW Feb. 16, 1960 Filed Sept. 17, 1956 E J. DIEBOLD TRANSFORMER BYPASS CIRCUIT 5 Sheets-Sheet 2 A Tram 7:

Feb. 16, 1960 E. J. DIEBOYLD 2,925,547

TRANSFORMER BYPASS CIRCUIT Filed Sept. 17, 1956 5 Sheets-Sheet 3 -ZZ0 W 259a 5515 b- I Feb. 16, 1960 E. J. DIEBOLD 2,925,547

TRANSFORMER BYPASS CIRCUIT Filed Sept. 17; 1956 5 Sheets-Sheet 4 Feb. 16, 1960 E. J. DIEBOLD 2,925,547

TRANSFORMER BYPASS CIRCUIT Filed Sept. 1'7, 1956 5 Sheets-Sheet 5 Q g: k i '8 I BY mM A Twi /12% United States Patent TRANSFORMER .BY PASS CIRCUIT Edward John Diebold, B'everlyHills, Calif, assignor to I-T-E Circuit 3 Breaker Company, Philadelphia, Pa., a corporation of Pennsylvania Application September .lfl, 1956, Serial No. 610,344.

19 Claims. (Cl; 3211-48) now U.S. Patent No. 2,756,380. issued July 24, 1956,40

Edward]. Diebold, utilize an electrical contact which is operated between an engaged and disengaged position in.

synchronism with theinput frequencyito achieve a unidirectional output to a DI-C. load.

It isessential that these contacts close and open on as small'a current as possible, if appreciable contact life is to be achieved, and to this end, a,commutating reactor,1.

which is a reactorhaving. a. relatively low magnetizing current, is connected in .series with the. contact. In operation, the commutating reactor is unsaturated. at the time of contact operation to afford a low current step and thereafter is saturated .to present substantiallyzero ,im-

pedanceto the series connected circuit- However, even the relatively low magnetizing current of the commutating reactor is too high for a contact to continuously interruptwithout.eventual contact destruction; Therefore, great eiforts have been made in the past to provide so-called pre-excitation circuitsforthe commutating reactor, which, as may be seenin copending application Serial No. 301,880 operate to compensate for .the magnetizing current of the commutatingareactor during its unsaturated interval and thereby substantially decrease the current throughlthe contact duringthe period of unsaturation.

In addition to the pre-excitation cir'cuit,which achieves almost perfect compensation, contacts of. devices such as contact converters are provided with a-bypass circuit which is'also-known as a spark extinguisher circuit;

Theby pass circuit is operative to act. as a shunt across the contact during contact disengagement so that the residual current carried by thecontact during disengagement may be shunted into the bypass circuit. Clearly, it is important that the.;by-pass circuit presents a low impedance and particularly a lowinductance to the residual current at the timeof contact disengagement .to prevent the appearance ofa high voltage drop across the separating contacts.

However, when the contact is open and reverse voltage appears across the open contact, a low impedance bypass circuit would short-circuit the contact. Hence, it is essential that for this condition, the by-pass circuit has a very high impedance.

Hence, a by-pass circuit must servepthe dual function of having a lowirnpedance. whilethe contact disengages and a very high'impedance after disengagement,

By-pass circuits of' this type may be seen in copendi'ng application Serial No. t90,319, filed February 24,1955,

0.. V 7 the-parallel circu t to buck down the by-pass rectifier Patented Feb. 16, 1960 wherein a reactor is utilized to maintain a current in the by-pass circuit. While this circuit is an effective one, the size of the required reactor may become economically prohibitive- Furthermore, the .space and heat dissipation requirement of such. reactors .poses other practical problems.

The-principle .of my invention is to provide .a-by-pass circuit wherein magnetizing current-of: the main com mutating reactor can flow in parallel with a series :connection .of the contact and an auxiliary commutating reactor which is constructed as .to have a substantially negligible magnetizing current, this .by-pass circuit consisting of the A.-C, terminals of a bridge-type single-phase semiconductor rectifier; the D.-C. side of which is connected to a transformer secondarywinding and a resistor. A by-pass circuit consisting of a bridge-typejrectifier with a D.-C..load circuit-consisting of a secondarytransforrner winding and a resistor in series in accordancewith my invention. will have a.high impedance wheneverthe'transformer voltage is in opposition to the normal rectifier output current, or when the rectifier output current is equal or larger than its output current.

When the input to the bypass rectifier .(its A.-C. terminals) carries. a current whichis lower than the current supplied by the transformer winding through-the resistor to the output sideof the rectifier, the impedance is very low. In the above case, the high impedance value-is equal to theresistance of the resistor, whereas the low impedance. value is given'by the differential resistance of the semi-conductor cells which may be very low.

By connecting the by-pass circuit in parallel with the seriesconnected auxiliary commutating reactor and contact, it is seen that a very low voltage will appear across the auxiliary commutating reactor prior to contact disengagement-sinceat this time the by-pass circuitimpedance is very low. Hence, the auxiliary commutating reactor -.will be demagnetized very slowly and its magnetizing currentwill substantially be at the static value which can be very easily compensated.

Furthermore, the. voltage appearing in this auxiliary commutating reactorisalways the same and can be made to have a small constant value.

It is of importance to note that my novel .by-pass circui-t can be applied in the absence of complex pre-excitation circuits or straightener circuitsof thetype set forth in.U.S. Patent No. 2,860,301,. issued November 11,1958, for the main commutating reactor.

Furthermore, my novel by-pass circuit maybe used without interfering with the operation .of their auxiliary circuits such as the fiux reversal circuit shown in copending applicationSerial No. 423,358, filed April 15, 1954,

now Patent No. 2,860,301,

'Accordingly, a primary object of my invention is toprovide aby-pass circuit for electrical contacts.

Another object of my invention is to provide a by-pass circuit for the contacts of a contact rectifier.

'auxiliary commutating reactor in series with an electrical contact and tothen provide. a parallel circuit including "a" rectifier having current flowing therethrough whereby the auxiliary commutating reactor forces current which would normally flow throughthe contact to flow through current.

when taken in conjunction with one of the by-pass circuit rectifier of Figure-2. i

tioned.

These and other objects apparent from the following description when taken in conjunction with the drawings in which:

- Figure 1 shows a schematic diagram of a three-phase mechanical rectifier 'to' which my novel. by-p'ass circuit may be applied.

Figure 2 shows an embodiment of rnyv novel invention phase of the circuit of Figure 1. E .1

Figure 3 shows the rectifier used in the by-pass circuit of Figure'Z in conjunction with its operatingvoltages and currents; 1

Figure 4 is'a graphical representation of the operation Figures 5a through 5f show the voltage and current variations as a function of time for the by-pass-circuit of Figure 2. 7

Figures 6a through 6d show the voltage and current variations as a function of time for the operation ofthe by-pass circuit of Figure 2, when taken in conjunction with its flux reversal'circuit. t Figures 7a and 7b show a possible simplification in the construction of the circuit of Figure 2. Figures 8a and 8 b show the simplification of the circuit of Figures 7a: and 7b in conjunction with 'theflux reversal circuit. E r I Figure 9 shows theapplication of'my novel invention to a complete six-phase rectifier circuit.

Referring now to Figure '1, there isseen one possible basic circuit for a three-phase contact rectifier. Phase A of the device is seen to comprise commutating reactors 11 and 12 and contacts 15 and 16, wherein the commutating reactor 11 and contactlS'are connected in series with the pcs'itive'output terminal'17' and commutating reactor 12 and contact 16 are connected in series withithe negative output terminal 18. j

The phases identified as phases B and C in Figure 1 are constructed in an identical manner to phase A.

1 Further details on the construction of the commutating reactors 11 and 12 and the contact devices Hand 16 and the operation thereof, may be had with reference to copending application Serial No. 301,880 as well as copending application Serial'No. 423.358;

Figure 2 shows phase A of Figure 1 with the applica: tion of my novel by-pass circuit.

The commutatingreactors 11 and Ham morespecificallyshown as comprising cores 23 and 24 respectively which are constructed of a highly saturable type material. Cores 23 and 24 may be provided with pr'e-excitation windings 25 and 26 which are energized from arsourc'e of v pre-excitation energization 27. They are further pro vided with flux reversal windings '28 and 29which serve to operate as a regulating means for the rectifier, these windings 28 and 29 being energized by a flux reversal circuit which will be more completely described hereinafter. a

It is then seen that the main windings 21 and 22 of the commutating reactors 11 and 12 are connected in series with the contacts 15 and 16 'of the rectifier which are driven into and out of engagement with one another by an operating means which may be seen with reference to copending application Serial No. 301,880 above men- The by-pass circuit of my novel invention comprises the componentsshown generally at 13 and 19in the phase containing commutating reactor 11 and the components shown generally at 14 and 20 of the phase containing the comm'utating reactor 12. More specifically, components of my invention will become 7 Component 19 is seen to be a full wave bridge connected rectifier containing diode elements 37, 38, 39 and 40 which may be of the germanium type. Similarly, component 20 is a rectifier bridge of the same type as the bridge 19 and contains the rectifier elements 41, 42, 43 and 44.

The A.-C. terminals of each of the bridge rectifiers 19 and 20 are then seen to be connected in parallel with the series connection of the saturable reactor windings 30 and 31 respectively and the contacts 15 and 16 respectively. The D.C. terminals of each of the rectifiers 19 and 20 are then energized by the output of the secondary windings 47 and 48 of transformer 51 which is energized at the terminals 52 and '53 of the primary winding 50. Resistors 45 and 46 are provided in series with each of the respective rectifier circuits coming from the secondary windings 47 and 48. V z I In order to describe the operation of the circuit of Figure 2, component 19 is repeated in Figure 3. In each branch of the bridge 19 of Figure 3 a current marked i i i and i flows through the diode elements 37, 40, 3.8 'and 39 respectively. Similarly, each rectifier element 37, 40 and 38 and 39 has a voltage drop shown as a voltage 2 e 2- and e respectively.

A current i isthen seen to flow into the junction between the rectifiers 37 and 38 and flows away from the junction between the rectifiers 39 and 40, while another current 11, flows into the bridge Iat the junction; between 13an'd l4 are saturable reactors having cores 32 and V respectively which have windings 30, 34 and 31,135 re. spectively.', Satu'rable reactors 13 and 14 are:t hen con structed in such amanner that the magnetizing current "of the windings'30,-and31.is smallertha'nithetnagnetizing current of the corresponding 'commutating lugs 21 and 22 of the cornmutating reactors reactor i1 and i2.

the rectifiers 37 and 39 and flows out of the bridge at the junction between the rectifiers 38 and 40. The importance of these outside currentsj and i can be seen in Figure 2 where the current i is the magnetizing current of the commutating reactor 11 which bypasses the contact 15. The

current i is provided by the transformer winding 48 and flows in series with the bridge 19 and resistor 45.

It is important to note that the two currents [i and i I are provided by different sources and both flow through the same rectifier circuit. More precisely, the current i 'is a direct current flowing through the two branchespf the'rectifier 19 and is independent of the current i3 because a direct current can flow through a rectifier in the forward direction in any magnitude and is not hampered by the fact that there is a rectifier in the circuit. On the other hand, the current 11; is provided from a voltage imvressed from the outside and can flow through the rectifier 19 according to the impedance of its D.-C.-branch iwhich is given mainly by' the resistor-45 and the voltage impressed on the winding 48 of the transformer 51.

Figure 3 also shows. five equations (Equations 1 l'through 5) connecting the'voltages and the current a ithrough e and i through i fthese equations being derived from a simple application of Kirchhofif s laws.

Figure 4 plots Equations 1-5 of Figure 3'with'respect to a typical diode characteristic of the diodes" used in rectifier 19 where the current values are plotted on the ordinate and voltage values are plotted on "theabs'cissa. From the voltages and currents shown in Figure 4, it is seen that the overall voltage drop a in the direction .of the by-pass current is the relatively small voltage difference between the voltages e, or a and e ore as may be seen from Equation 3 of Figure 3.

On the other handQthe voltage e is a much larger Voltage drop. The rectifier circuit therefore has the property that one circuit, which is the one supplied by the transformer 51 supplies the voltage drop for the current i which comes from another circuit. If the voltage drop in the circuit is to be further reduced and the current i is approximately the same value,.it is possible to select the diodes accordingly in such a way that thediodcs 38 and 39 which are subjected to the'larger current i and i have ai -lesser voltage drop than the diodes 37 and 40. Practically, this can be easily done because the diodes .38 and 39 ha,ve to carry a larger current and can there- 0 1 i fg r area diodes whereastheles 3" which carry only a. smell current can be muses when diodes. This deliberate mismatch will provide an even smallervoltage drop e over the whole by-pass rectifier.

It is to .be noted. that the purpose of Figure. 4.is merely to effect a solution of Equations 1 through 5 givenin Figure 3 for the voltage e That is-to say, it is necessary to. resort to graphical means for a solution of this type inview of the non-linear naturerof the forward voltage drop characteristic of the rectifier 19.

The flux reversal circuit shown in Figure 2 comprises the flux reversal windings 28 and 290i thercommutating reactorsll and'12, transductors 54 and 55, a power source including the transformer 65 which is energized at terminals 6667 and a biasing means which is energized from the terminal 64.

More specifically, the transformer 65 is connected in such a manner as to be connected in series with the flux reversalwinding 28, winding 58of transductor 54, and rectifier 62' while a parallel'circuit is provided which includes the flux reversal winding 29, transductor winding 59 and'diode 63. Theconnection of diodes 62 .and 63 permits current to flow alternately through one branch or theother branch of the circuit. V

The transductors 54 and 55 which are shown as having coresof saturable type material 56 and 57 respectively are provided with biasing windings 60'and 61 which are energized by the biasing source 64.

The operation of this circuit is as follows;

When the potential of the source 65 is in a direction to pass current through the diode 62, it isseen that the volt seconds impressed across the winding 28 will be,

determined by the time at which the reactor 54 saturates, which'in turn is dependent upon the'biasing at the biasing winding 60. In thereverse direction, that is when the source 65 reverses, the reversal of flux in the core '54 is dependent upon the semi-conductor 62 as well as the;

level of the bias in the biasing winding 60; The reverse voltage of transformer 65 appears on winding 58 as long as the current is in a direction of the diode 62. As soon as this current 'wants to reverse, then the voltage of the transformer 65 appears on the diode 62.

in this reactor core 56, which" in turn must be shiftedinto the opposite direction during the next successive positive cycle of the voltage in transformer 65; Hence, the flux in the core 56 must first'be reversed by means ofvoltage appearing on the winding 58 before the remainder of the voltage can appear on winding 28.

This system of'fiux reversal has the advantage that the control current provided by the source 64 is a direct currentand that this direct current is of very-small magnitude and can be provided by a source of extremely low voltage. On the other hand, the poweroutput of the flux reversal circuit itself'is provided by the power coming from the transformer 65. Therefore, a high amplification is obtained from the power source 64 to the power output into the windings 28 and 29. Another stage of power amplification then occurs between the input'of the commutating reactor, that is the flux reversal windings 28 and 29, to' the output of the mechanical rectifier on the terminals 17 and 18.

Figures 5a through 5 f specifically illustrate the manner in which the circuit of Figure 2 operates, wherein Figureduring the time that commutation actually.occursbetweenthe phase A and B. For this reason, the comrnutating voltageis shown only asadottedline because for themost ofthe-cycle the contact, 15, is open and this commutating voltage appears across the contact 15.

During the break step or contact disengagement interval, the commutating voltage appears on the commutating reactor Hand is shown as e in the Figure 51;. Applying avoltage like a to the commutating reactor winding 21 will cause a certain magnetizing current. Assuming thatthere is no pre-excitation current in the winding 25 and that during this time the current through the winding 28 is zero, the current flowing through the winding 21 will be given vby the magnetizing current required tomagnetize the core 23; This current is shown asj in Figure 5b. The current z' is, atypical magnetizing currentofa saturable core reactor containing a nickel iron corehaving a so-called square hysteresis loop. The current is, however, variable enough during this step .tobehard to compensateby means of a constant current.

Figure 5c shows two heavylines i and i which show the magnetizing current of the commutating reactor for thelongest or earliest break step i and the shortest or latest break step i The actual position ofthis step will be determined by the voltage regulation of the rectifier.

In the normal operation of the mechanical rectifier, the steps will never be longeror earlier or shorter or later than these two extreme values. The current i is always larger inmagnitude than the current i because it is caused by a higher voltage and a faster magnetization. The values shown in Figure 50 however show that there is only a small difference, in the actual current values.

' The dotted lines around the two current curves of Figure, Scare .the voltage curves which are taken from the dotted voltage lines in Figure 5b. They are marked as 2 for-the commutating voltage during the break step on the commutating reactor during the longest break step ande as .the commutating voltage during the break step of the shortest break step.

The solid line'in Figure 50 marked as L; is the current which is provided from the outside current source of the transformer 51 into the by-pass circuit of Figure. 2. The current 11; of Figure 5c is deliberately made larger than the largest magnetizing current available in the full range between the longest and the lowest step to the shortest and highest step. For this reason, Figure 5c shows the .two extreme cases simultaneously and is not aphysical representation of one process.

Figure 5b shows an example of one particular step current i .whichcorrcsponds to the operation .shown in Figures Sd- Sf.

It was seen in Figures 3 and 4 that the by-pass rectifier 19 will have a very low voltage drop as long as thecurrent i is smaller than the. current i From Figure, 5c, itis seen that the current i or i is the current provided by the commutating reactor which flows either through the contact 15 or the by-pass rectifier 19. 'If the current through contact 15 is to be held at zero, then the full current of the commutating reactor i must flow through the bypass rectifier 19. As seen in Figure 5c thiscurrent i is always lower than the current i,, and the. condition described in Figures 3 and 4 is met. Hence, by providing a current i; which has the shape shown. in Figure 5c, the conditions of the by-pass circuits will be fully met and the voltage e which is the voltage drop 01? the by-pass circuit will be extremely small as demonstrated in Figure 4. In a practical case, if, the current i has a value of three amperesas shown in Figure 4, the voltage drop 2 is equal to .34 volt.

Figure 5d shows the voltage, e appearing across the contact 15 and, as a dotted line, the voltage e which is the voltage induced in the winding 48 of transformer 51. Thevoltage appearing on resistor45 therefore, will be the rectifier voltage e plus the voltage e 'rectifi'ed.

Adding these twovoltages gives the curve e of Figure also a measure of the current i; because of the resistive nature of the resistor 45 and the solid line of Figure e .therefore also shows the current i a Figure 5f finally shows the division of currents between the contact, parallel circuit and commutating reactor. The solidline i is the current flowing through the by-pass circuit and is actually the current which should be taken away from the contact 15. The dotted line i -l-i in Figure 5] is an internal current in the by-pass circuit which has no equivalent on the outside. sum of the'current i plus the dotted current i +i is equal to the current i as may be seen from Equation 1 of Fig- The ure 3. Hence, i will be smaller than the current A, if

i +i .is .diiferent from. zero during the whole of the break step as shown in Figure, Si and the by-pass circuit will operate as is desired.

If the by-pass circuit of Figure 2 operates as described in Figures Sa -5f, then its voltage drop (2 of Figure 4 will be extremely smalL. Having a verysmall voltage drop on the by-pass circuit 19 means that during the gangsta break step an extremely small voltage drop appears on 'the winding 30.0f the auxiliary commutating reactor 13. This means that a voltage of 400 to 500 volts may appearon, the winding 21 of commutating reactor 11 while a voltage of only approximately of a volt will appear on the winding 30.

It is interesting to note that this low voltage is practically'independent of the time of operation of the rectifier because this voltage is only caused by the drop of the voltage on the rectifiers on the'bridge 19 by means of the current which can vary in the range between i; and i shown in Figure 50. Because these currents are inherently approximately constant, the voltage drop is subject to very small variation as may be seen in Figure 4. Hence, the voltage appearing 'on the coil of the auxiliary commutating reactor 13 is almost constant and very small. 7

Therefore, the commutating reactor 13 operates nearwinding 3%), which is thefcurrent that must be broken by a the contact, is practicaily zero. Furthermore, since this currentis obtainedas a difierence between an almost staticflmagnetizing current in a small comm'utating' reac-' .tor subjected to a small and almost constant voltage,

which does not change with the load condition of the rectifier or the impressed voltage on the rectifier, the compensation 'of'this current. can be made almost perfect.

It isalso seen that when the contact 15 of Figure 2 opens, therecovery voltage across the contact is only that voltage drop due to the flow of by-pass circuit current; Itwas seen in Figures 511-5 that the whole of this. by-pass current flows through the by'pass circuit causing only a negligibly small voltage drop of a'fraction of a volt. This small voltage drop is thefull recovery g voltage across the contact and a higher recovery voltage across the'contact can not occur as long asthe break step lasts. Q

.My novel by-pass circuit, therefore, allows interruption of thecontact of a contact rectifier under substantially zero voltage and current conditions. pensation will befafiorde'd under any condition of. load Q r the magnitude of the magnetizing current andof the go or ph e' control?" anee it is independent of This comspeed of magnetization in the main commutating" reactor and dependent only because on an auxiliary commutating reactor which is subjected to a load condition of an auxiliary rectifier. V 7

Figures 6a-6d show the operation of the flux reversal circuit of Figure 2 and demonstrates the manner in which my'novel by-pass circuit cooperates with the flux reversal circuit.

In Figure 6a the phase voltages of Figure 5a are repeated for convenience and Figure 6b shows the current i, which fiows through the'commutating reactor winding 21. Figure 6c shows the voltage 2 impressed by the flux reversal transformer 65 upon the flux reversal circuit consisting of the flux reversal winding 28, transductor 54 and the semi-conductor 62. In the first, negative half wave of voltage e the'diode 62 blocks. However, since there is a direct current flowing through the winding 60 of transductor 54, the current through winding 58 is not quite zero and the voltage e 5 appears on the winding-'58 until the. current i has died down to Zero. This current is shown as in, a dotted line in Figure 6a. The dotted line f x shows the same current magnified one hundred times, showing the effects of the small magnetizing current of the saturable core 56. Therefore, in the first part of the negative half-wave, the voltage e appears e of Figure 60 on the winding of the transductor 54.

In the latter part of the cycle, after the vertical dotted line in Figure 6c, the transductor 54 cannot absorb any more voltage because its magnetizing current istlarger than the negative bias in the winding 64], i.e., i would become negative except for diode 62, which means that now all the voltage of the transformer 65. appears on the .diode 62 asis'shown by the voltage 2 in Figure 6c.

- In the successive positive half-cycle, the voltage 2 is again applied to the same components but'almost no positive current i can flow until the flux of the transduct'or 54 has been returned to the positive direction as shown in Figure 6a. Therefore, the voltage 2 now appears in the opposite direction on transductor 54 astis shown as the positive shaded area of Figure 6c.

When the transductor core 56 saturates in the forward direction, the remaining voltage of the transformer 65 applies itself to the winding 28 of the commutating reactor because the diode 62 cannot absorb any voltage in this direction. A part of this positive voltage also is absorbed by the resistive voltage drop of all the components because now a substantial current flows in a forward direction, this resistive voltage drop being shown as he in Figure 6c. In a practical case, however, this resistive voltage drop isvery small and may be neglected. ..Hence, the flux of the commutating reactor core 23 is reversed by a predetermined amount by the voltage 2 of Figure 6c and determines the amount of fiux which is available for the next step and therefore controls the output voltage of the mechanical rectifier.

Figure 6d shows the flux reversal current i in .the winding 28. The current 1' shown as a dotted line, is the actual magnetization current of the commutating reactor core during the flux reversal interval. This current is a step current occurring when a variable voltage is impressed, such as a voltage e shown in Figure 6c. Thecommutating reactor under these circumstances, however, is a transformer because the voltage e which appears on the winding 28 is transformed into the winding 21 and therefore appears as an. additional voltage to the reverse voltage of the rectifier as well as on the bypass circuit which contains the resistor 45. This may be seen in Figure 52 where the voltage e contains a cornponent due to the flux reversal shown as a sharp peak towards the end of the wave.

This peak is a direct effect of the flux reversal and .causes aresistive current in the resistor 45. An additional current 11;; must therefore besupplied by the fiux reversal circuit as-is shown in Figure rt'bya dot-dash line. "The total flux reversal current the'n assumes the from atfecting the two cores according to the compensa- I shape ofv i shownas a solid line in Figure 6d. This total flux reversal'current therefore is the. sum of amasnetizing current and a resistive current.

Therefore, the operation shown in Figures 6a-6d is the operation of a magnetic amplifier reversing the flux of a commutating reactor. However, the commutating reactor is shunted by a resistor. At first sight, this seems to be a disadvantage because this requires more power of the transformer 65. However, this power is very small compared to the power of the mechanical rectifier. On the other hand, resistive shunting of the flux reversal circuit has the very great advantage of providing additional damping of the magnetic amplifier which reduces the possibility of instabilities andrenders the control more linear. It should be noted that in many applications of magnetic amplifiers the output circuits are in fact shunted with resistors in order to render them more linear and more stable. In this case, the bypass circuit introduces a resistive by-pass to the flux reversal circuit which is not necessarily a disadvantage.

In my copending application Serial No. 412,165 filed February 25, 1954, and now abandoned, I describe a method whereby two separate reactors may be replaced by a single reactor having two cores and a single windin'g. This novel construction may be-utilized in the in- .stant invention as seen in Figures 7a and 7b.

Figure 7a shows the-reactorslland 13.as they are connected in Figure 2. These reactors have the main windings 21 and respectively and the cores 23 and 32 respectively. 30

In Figure 7b in accordance with the constructionset forth in above noted U .'S. Patent No. 2,756,380, the twocores are arranged concentricallyand have the common winding 21. Winding 21 therefore, also serves as the winding 30, this beingindicated by placing number 30 in parentheses.

The current i; now flows. through the common winding 21 and magnetizes both the cores 23 and 32. However, the core 32 should be magnetized only by the current i, which is the difference between the currents i and i 40 This can easily be compensated for by a negative winding 70 of the same number of; turns as-the winding 21. The current i;.; then demagnetizes the core 32 by the same amount as it did when flowing through thewinding 21.

It canbe shown by. more thorough analysis that the, 4-. voltage and current conditions of these two arrangements of coils are absolutely identical and equivalent.

Figure 8a shows, in essence, the-flux reversal circuit seen in Figure 2. This flux reversal circuit consists merely of the transformer 65 energizing the parallel circuits containing diodes 62 and 63 respectively, transductors 54 and respectively, flux reversal windings 28 and 29 respectively, and the transformer 65 is then connected between the main power windings,28 ,and 29;and the function between the di0des62 and 63.

In order to prevent reversal of the-flux in the cores 32 and 33 of.the auxiliary commutating reactors if they are connected according to Figure 7b, thewindings and 72 arealsoused-to prevent the flux reversal current 60 tion described in Figure 7b. This then results in the circuit connection of Figure 8b which is absolutely equivalent tothe Figure 8a, except that it eliminates the flux reversal winding on the commutating reactors.

Figure 9 showsa complete threephase double Way rectifier usingboth theby-pass circuit and flux reversal circuit described heretofore. In Figure 9, A.C. terminals 73, 74 and 75 are connectedto energize the three-phase power transformer 76. Each phase is provided with commutating reactors 77 through 82 respectively, which are connected in series with mechanical rectifier contacts 83-.through 88 respectively, and appropriate connections are made to the D.-C. terminals 90 and 91. in accordance with the construction of Figure 8b, fiux reversal is provided by.transductors 92 through 97, which work in conjunction with thediodes 98 through 103. The operation of'this flux reversal'circuit is the same as described in Figure 6 for the circuit of FigureZ.

In addition to the fiux reversal circuit, a by-pass circuit of the type shown in Figure 2 is provided and consists of the rectifier circuits 104 through 109 and the resistors 110 through 115.

It was seen in Figure 2 that power supplies for the flux reversal circuit and the by-pass circuit required the transformers 51 and 65. The transformer 51 of Figure 2 consists of a three winding transformer with the primary winding 50 and the secondary windings 47 and'48. Since windings 47 and 48 carry direct currents which are in opposition, the transformer core 49 is not magnetized by unidirectionalcurrent but the transformer is a true A.-C. transformer. Hence, it is possible to transform a pure A.-C; voltage that has been appearing between the terminalsv52 and 53 into two direct current circuits without saturating the transformer core.

The transformer 65 is also a true transformer because it also feeds two diode circuits which are connected in opposition. Therefore, in the circuit of Figure 9, instead of having two transformers per phase, which for ath'reephase system.would require a total of six transformers, a single transformer 116 may be utilized. Transformer I16 consists of a primary winding 117 connectedin polygon whereby the polygon connection serves to obtain a15 phase shift from the main transformer 76. The secondary windings .118 are connected in three independent single phase windings each having a single phase voltage displaced by from the voltage in the adjacenfwindings, These transformer windings each correspond to a transformer winding such asthe secondary winding of transformer65 in Figure 2..

The winding's119j and 12 0a,re again two, groups of three single phase-windings each bjeing energizedjby the same primary winding117. Hence, a' single three phase transformer structure 116'serves to supply all o fjthe power requirements forthe by-pass andfiux reversal circuits.

More specifically, the transformer 116 has five different windings on eachleg. Two windings make up the windings of the primary winding 117, one being a long winding and the other being a short winding, The secondary, tertiary and quaternary windings 118, 119 and 120 each require one winding on the same leg. This is true for all three phases, the transformer then having three legs with, five windings each. The secondary winding 118 feeding thefiux reversal circuit has a voltage which isin the same phase relationship as shown in Figure 6, The tertiary winding 119 and the quaternary winding 12!) feed the hy-pass circuit with a voltage which is in phasewithayoltage such ,as voltage 2 of Figure 5. These, voltages are alsoirr phase with, the voltage shown ,to be,,provided, by the; transformer 116inuFigure 92' It should benoted thatthe flux reyersal voltageQofFigugeS and the voltage requiredto drive theby-pass circuit of Figure 6 are not in phase but are,180' out of phase. This phasing ,of 180 however, is easily obtained because the windings'are open and can be connected in any way asis desired in the circuitry,

The control windings of transductors 92 through 97 are energized through the rheostat 121 and smoothing choke 122 and rectifier 123. D.-C. bias is applied to the cores of the maincommutating reactor and auxiliary commutating reactors at the windings 124 through 129. These windings are in turn fedithrough the rheostat and the choke 131 from the same rectifier 123. It shouldbe noted that eachof these pre-excitation windings has a small number of turns around both commutating reactor cores and an additional number of turns around the inner commutating reactor core which pertains to the auxiliary commutating reactor. This different magnetization affords compensation for the partial amount of the main commutating reactor magnetizing current andthe magnetizing current of the auxiliary commutating reactor. This different compensation of magnetizing current is possible because in the mam commutating reactor the magnetizing current varies between a a minimumand maximum value and compensation is possible for the minimum value and no more.

On the other .hand, on the auxiliary commutating reactor compensation can be made for the full amount of the magnetizing current as was described in the discussion of Figure 5.

The novelcircuitry set forth in Figure 9 has further structural advantages in the practical rectifier unit. That is a minimum number of terminals are required for the auxiliary circuits inserted in closedtanks through which .filtered oil is circulated and nitrogen under pressure is on top of the oil; Bushings which must carry the main cur-' rent or' auxiliary currents to the transformer tank are subjected to leaks, and, if they leak, the nitrogen under pressure expels' the oil at a very great rate. The circuits undenquestion, however, can provide complete flux re- "versal and compensation of the magnetizing current of each commutating reactor by adding only one auxiliary lead per commutating reactor. This leads to a system having only a few bushings for the transformer and compares very. favorably with prior circuits which require up to ninety auxiliary bushings for one transformer tank.

Although I have described preferred embodiments of my invention, many-variations and modifications will reactor connected in series with said contact and a rectifier means connected in parallel with said series connected saturable reactor and contact; said rectifier being connected in series with a voltage source and an impedance; said voltage source being connected to pass current through said rectifier before said contact is moved to open said electrical circuit to provide a low impedance path for current flow in said by-pass circuit; said rectifier being connected in a direction to block said current flow in said bypass circuit.

2. A by-pass circuit for an electrical contact; said electrical contact being movable to open and close an electrical circuit; said by-pass circuit comprising a saturable reactor connected in series with said contact and a rectifier means connected in parallel with said series connected saruable reactor and contact; said rectifier being connected in series with a voltage source and an impedance;'said voltage source being connected to pass current through said rectifier before said contact is moved to open said electrical circuit to' provide a low impedance path for current fiow in said by-pass circuit;'said rectifier being connected in a direction to block said current flow in said bypass circuit; the impedance of said by-pass circuit when said contact is open being substantially that of said impedance connected in series with said rectifier means.

3. A by-pass circuit for an electrical contact; said electrical contact being movable to open and close an electrical circuit; said by-pass circuit comprising a saturable re- "actor having a substantially negligible low magnetizing current connected in series with said contact and a rectifier means connected in parallel with said series connected saturable reactor and contact; said rectifier being connected to block the flow of current through said contact prior to contact opening; said rectifier being connected in series with a voltage source and an impedance; said voltage source being connected to pass current through said rectifier before said contact is moved to open said electrical circuit to provide a low impedance path for current flow in said lay-pass circuit.

4. A by-pass circuit for an electrical contact; said electrical contact being movable to open and close an electrical circuit; said by-passcircuit comprising a saturable reactor connected in series with said contact and a single phase bridge connected rectifier; the AC. terminals of said rectifier being connected in parallel with the series connection of said saturable reactor and contact; an alternating voltage source and a resistor; said alternating voltage source and said resistor being connected in series with the D.-C. terminals of said rectifier.

5. A by-pass circuit for an electrical contact; said electrical contact being movable to open and close an electrical circuit; said by-pass circuit comprising a saturable reactor connected in series with said contact and a single phase bridge connected rectifier; the A'.-C. terminals of said rectifier being connected in parallel wtih the series connection of said saturable reactor and contact; an alternating voltage source and a resistor; said alternating voltage source and said resistor being connected in series with the D.C. terminals of said rectifier; said alternating voltage source being connected to pass current through said rectifier before said contact is moved to open said electrical circuit to thereby provide a low impedance path for current flow in said by-pass circuit; the impedance of said by-pass circuit when said contact is open being substantially the resistance of said resistor.

6. A by-pass circuit for a contact connected in series with a commutating reactor; said contact being movable between an open'and a closed position; said commutating reactor being constructed to provide a low current step within which said contact is disengaged; said by-pass circuit comprisingan auxiliary commutating reactor having a magnetizing current substantially lower than the magnetizing current of said commutating reactor connected in series with said contact and a rectifier; said rectifier being connected in parallel with said series connected auxiliary commutating reactor and contact; said rectifier being connected in series with a voltage source and an impedance; said voltage source being connected to pass current through said rectifier before said contact is moved to open said electrical circuit to provide a low impedance path for current flow in said by-pass circuit.

7. A by-pass circuit for a contact connected in series with a commutating reactor; said contact being movable between an open and a closed position; said commutating reactor being constructed to provide a low current step within which said contact is disengaged; said by-pass circuit comprising an auxiliary commutating reactor connected in series with said contact and a single phase bridge connected rectifier; the A.-C. terminals of said rectifier being connected in parallel with the series connection of said auxiliary commutating reactor and contact; an alternating voltage source and a resistor; said alternating voltage source and said resistor being connected in series with the D.-C. terminalsof said rectifier.

8. A by-pass circuit for a contact connected in series with a commutating reactor; said contact being movable between an open and a closed position; said commutating reactor being constructed to provide a low current step within which said contact is disengaged; said by-pass circuit comprising an auxiliary commutating reactor connected in series with said contact and a single phase bridge connected rectifier; the A.-C. terminals of said rectifier being connected in parallel with the series connection of said auxiliary commutating reactor and contact; an alternating voltage source and a resistor; said alternating voltage source and said resistor being connected in series with the D.-C. terminals of said rectifier; said alternating voltage source being connected to pass current through said rectifier before said contact is moved to open said electrical circuit to thereby provide a low impedance path for current flow in said by-pass circuit; the impedance of said by-pass circuit when said contact is open being substantially the resistance of said resistor.

9. in a contact converter for energizing a D.-C. load from an A.-C. source, said converter comprising the se --ries' connection of a commutating reactor, a' pair of cooperating contacts being synchronously operated between an engaged and a disengaged position, said A.-C. source and said D.-C. load; a by-pass circuit; said by-pass-circuit comprising an auxiliary commutating reactor having a magnetizing current substantially lower than the magnetizing current of said commutating reactor connected in series with said contact and a rectifier; said rectifier being connected to block the flow of current through said con tact prior to contact opening; said rectifier being connected in parallel with said seriesconnected auxiliary commutating reactor and contact; said rectifier being connected in series with a voltage source and an impedance; said voltage source being connected to pass current through said rectifier before said contact is moved to open said electrical circuit to provide a low impedance path for current fiow in said by-pass circuit.

10. In a 'multi-phase contact converter for energizing a DC. load from a multi-phase A.-C. source, each phase of said converter comprising the series connection of a "commutating reactor, a pair of cooperating contacts being synchronously operated between an engaged and a disengaged'position, said A.-C. source and said D.-C. load; a by-pass circuit; said by-pas's circuit comprising an auxiliary commutating reactor having a magnetizing current substantially lower than the magnetizing current of said commutating reactor connected in series with said contact and a rectifier; said rectifier being connected to block the flow of currentthrough said contact prior to contact opening; said rectifier being connected in parallel with said series connected auxiliary commutating reactor and contact; said rectifier being connected in series with a voltage source and an impedance; said voltage source being connected to pass current through said rectifier before said contact is moved to open said electrical circuit to provide a low impedance path for current fiowin said by-pass circuit; said rectifier being connected to block the flow of current through said contact priorto contact opening.

11. In a contact converter for energizing a D.-C. load from an A.-C. source, said converter comprising the series connection of a commutating reactor, a pair of cooperating contacts being synchronously operated between an engaged and a disengaged position, said A.-C. source and said D.-C. load; a by-pass circuit; said by'-pass circuit comprising a saturable reactor connected in series with said contact and a single phase bridge connected rectifier; the A.-C. terminals of said rectifier being connected in parallel with the series connection of said saturable reactor and contact; an alternating voltage source and a resistor; said alternating voltage source and said resistor being connected in series with the D.-C. terminals of said rectifier; said rectifier being connected to block the flow of current through said contact prior to contact opening.

12. In a multi-phase converter for energizing a D.-C. load from a multi-phase A.-C. source, each phase of said converter comprising the series connection of a commutating reactor, a pair of cooperating contacts being synchronously operated between an engaged and a disengaged position, said A.-C. source and said D.-C. load; a by-pass circuit; said by-pass circuit comprising a saturable said by-pass circuit when said contact is open being substantially the resistance of said resistor.

13. A by-pass circuit for an electrical contact; said electrical contact being movable to open and close an electrical circuit; said by-pass circuit comprising a saturable reactor connected in series with said contact and a single phase bridge connected rectifier; the A.-C. terminals of said rectifier being connected in parallel with the series connection of said saturable reactor and contact; an alternating voltage source and a resistor; said alternating voltage source and said resistor being connected in series with the D.-C. terminals of said rectifier; said alternating voltage source being connected to pass current through said rectifier before said contact is moved to open said electrical-circuit; the voltage drop across the A.-C. terminals of said rectifier bridge being the difference between a first voltage drop on first rectifier diodes of said bridge carrying by-pass circuit current and current due to said voltage source in the same direction and a second voltage drop on second rectifier diodes of said bridge carrying by-pass circuit current and current due to said voltage source in opposite directions.

14. A by-pass circuit for an electrical contact; said electrical contact being movable to open and close an electrical circuit; said by-pass circuit comprising a saturable reactor connected in series with said contact and a single phase bridge connected rectifier; the A.-C. terminals of said rectifier being connected in parallel with the series connection of said saturable reactor and contact; and alternating voltage source and a resistor; said alternating voltage source and said resistor being connected in series with the D.-C. terminals of said rectifier; said alternating voltage source being connected to pass current through said rectifier before said contact is moved to open said electrical circuit; the voltage drop across the A.-C. terminals of said rectifier bridge being the difference between a first voltage drop on first rectifier diodes of said bridge carrying by-pass circuit current resistor connected in series with said contact and a single phase bridge connected rectifier; the A.-C. terminals of said rectifier being connected in parallel with the series connection of said saturable reactor and contact; an alternating voltage source and a resistor; said alternating voltage source and said resistor being connected in series with the DC. terminals of said rectifier; said rectifier being connected to block the flow of current through said contact prior to contact opening; said alternating voltage source being connected to pass current through said rectifier before said contact is moved to open said electrical circuit to thereby provide a low impedance path tor current flow in said by-pass circuit; the impedance of and current due to said voltage source in the same direction and a second voltage drop on second rectifier diodes of said bridge carrying by-pass circuit current and current due to said voltage source in opposite directions; said first and second diodes of said rectifier bridge being constructed to make said first and second voltage drops substantially equal.

'15. A by-pass circuit for a contact connected in series with a commutating reactor; said contact being movable between an open and a closed position; said commutating reactor being constructed to provide a low current step within which said contact is disengaged; said by-pass circuit comprising an auxiliary commutating reactor connected in series with said contact and a single phase bridge connected rectifier; the A.-C. terminals of said rectifier being connected in parallel with the series connection of said auxiliary commutating reactor and contact; an alternating voltage source and a resistor; said alternating voltage source and said resistor being connected in series with the DC. terminals of said rectifier; the voltage drop across the A.-C. terminals of said rectifier bridge being the difference between a first voltage drop on first rectifier diodes of said bridge carrying by-pass circuit current and current due to said voltage source in the same direction and a second voltage drop on second rectifier diodes of said bridge carrying by-pass circuit current and current due to said voltage source in opposite directions.

16. A by-pass circuit for a contact connected in series with a commutating reactor; said contact being movable between an open and a closed position; said commutating reactor being constructed to provide a low current step within which said contact is disengaged; said by-pass circuit comprising an auxiliary commutating reactor connected in series with said Contact and a single phase bridge connected rectifier; the A.-C. terminals of said rectifier being connected in parallel with the series connection of said auxiliary commutating reactor and contactfan alternating voltage source ancl a resistor; said alternating voltage source andsaid resistor being con-' nected in series with the D.-C. terminals of said rectifier; the voltage drop across the A.-C. terminalsof said rectifier bridge being the difference between a first voltage drop on first rectifier diodes of said bridge carrying byfbridge being constructed to make said first and second voltage drops substantially equal.

17. In a contact converterfor energizing a DC. load from an A.-C. source, said converter comprising the series connection of a commutating reactor, a pair of cooperating contacts being synchronously operated between an -engaged-and a disengaged position, said A.-C. source and said D.-C. load; a by-pass circuit; said by-pass circuit comprising a saturable reactor connected in series with said contact and a single phase bridge connected rectifier;

the A.-C. terminals of said rectifier being connected in parallel with the series connection of said saturable reactor and contact; an alternating voltage source and a resistor; said alternating voltage source and said resistor being connected in series with the.D.-C. terminals of 1 said rectifier; said rectifier being connected to block the flow of current through said contact prior to contact .opening; the voltage drop across the A.-C. terminals of said rectifier bridge being the difference between a first voltage drop on first rectifier diodes of said bridge carrying by-pass circuit current and current due to said voltage 1 source in the same direction and a second voltage drop on second rectifier diodes of said bridge carrying bypass circuit current and current due to said voltage source in opposite directions.

18. In a contactconverter for energizing a D.-C. load from an A.-C. source, said converter comprising the series connection of a commutating reactor, a pair of cooperating contacts being synchronously operated between anengaged and a disengaged position, said A -C. source and said D.-C. load; a byV-pass circuit; said by-pass circuit comprising a saturable reactor connected in series'with said contact and a single phase bridge connected rectifier;

,the A.-C. terminals of said rectifier being connected iii parallel with the 'series connection-of said saturable reactor and contact; an alternating voltage source and a resistor; said alternating voltage source a and said resistor being connected in series with the D.-C. terminals of said rectifier; said rectifier being connected to block the flow of current through said contact prior to contact opening; the voltagedrop across the A.-C. terminals of said rectifier bridge being the difierence between a first voltage drop on first rectifier diodes of said bridge carrying by-pass circuitcurrent and current due to said voltage source in the samedirection and a second voltage drop on second rectifier diodes of said bridge carrying by-pass circuit current andcurrent due to said voltage source in opposite directions; said first and second diodes of said rectifier bridge being constructed to make said first and second voltage drops substantially equal.

19. In a multiphase system for exchanging energy between a multiphase A.-C. system and a D.-C. system, each 1 phase of said multiphase-AC. system being connected in'series with a synchronously operated contact, a commutating reactor and said D.-C. system; a by-pass circuit for each of said contacts; each of said by-pass circuits comprising an auxiliary commutating reactor having an nected in series with the D.-C. terminals of said bridge rectifier of another ofsaid multiphase systems, the D.'-C.

ampere turns of said first and'secondsecondary windings I being oppositely directed with respect to one another.

References'Citedinthe file of this patentv v UNITED STATES PATENTS 2,756,380 7 Diebold July 24, 7195s .72,75V 6,3.811 Rolf July 24, 1956 2,758,271 Rolf Aug. 7, 1956 2,834,932

Dew ey -L.---- ...May 13, 1958 

